In Net-ICal-0.15 module ETJ.pm line 316 change 'doc' to 'domain'.
categories => { # RFC2445 4.8.1.2 - optional in VEVENT, VTODO, VJOURNAL
type => 'parameter',
doc => 'ref',
options => 'ARRAY', # there can be more than one of these, just text
value => undef,
},
should be
categories => { # RFC2445 4.8.1.2 - optional in VEVENT, VTODO, VJOURNAL
type => 'parameter',
domain => 'ref',
options => 'ARRAY', # there can be more than one of these, just text
value => undef,
},